do mushrooms need fresh air to grow?

When the mycelium has fully colonised your grow bag/substrate, mushrooms are ready to fruit. They will need fresh Oxygen at this stage (O2). This is known as fresh air exchange (FAE) this is where CO2 is expelled and O2 is exchanged.

As mushrooms grow, they produce low levels of Carbon Dioxide (CO2), in order for them to keep growing healthy, they need to exchange this CO2 for O2. Usually a small slit cut in the bag where the mushrooms are forming is enough, as the mushrooms will grow towards the fresh CO2.

Sometimes they will even grow through the filter patch on the bag!

Cutting the top off the bag, and loosely folding over the top of the bag, securing it with a paperclip or clothes peg, to allow a small amount of fresh O2 into the bag is sufficient, Depending on the mushroom strain being grown.

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